Generally, in a mobile communication system, communication security may be ensured in a one-to-one communication environment between one terminal and its counterpart terminal. However, in a so-called group communication environment where a plurality of terminals communicate with each other in a group, inefficient use of resources, billing problems, security vulnerabilities and the like may exist.
In the group communication environment, the security vulnerabilities may be one of the factors to inhibit the use of the group communication. Therefore, there is a need for an efficient way to stably provide security services in the group communication.